Residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed

Residual stress may be desirable or undesirable

For example, laser peening imparts deep beneficial compressive residual stresses into metal components such as turbine engine fan blades, and it is used in toughened glass to allow for large, thin, crack- and scratch-resistant glass displays on smartphones

Residual stress

Destructive TechniquesThe destructive techniques are such that they result in a

large and irreparable structural change to the specimen, meaning that either the specimen cannot be returned to service or a mock-up or spare must be used

Contour Method - measures the residual stress on a 2D plane section through a specimen, in a uniaxial direction normal to a surface cut through the specimen with wire EDM.

Slitting (Crack Compliance) - measures residual stress through the thickness of a specimen, at a normal to a cut "slit".

Block Removal/Splitting/LayeringSach's Boring

Measurement techniques

Similarly to the destructive techniques, these also function using the "strain release" principle. However, they remove only a small amount of material, leaving the overall integrity of the structure intact. These include:

Deep Hole Drilling - measures the residual stresses through the thickness of a component by relaxing the stresses in a "core" surrounding a small diameter drilled hole.

Centre Hole Drilling - measures the near surface residual stresses by strain release corresponding to a small shallow drilled hole with a strain gauge rosette.

Ring Core - similar to Centre Hole Drilling, but with greater penetration, and with the cutting taking place around the strain gauge rosette rather than through its centre

Semi-destructive Techniques

The non-destructive techniques measure the effects of relationships between the residual stresses and their action of crystallographic properties of the measured material. Some of these work by measuring the diffraction of high frequency electromagnet radiation through the atomic lattice.spacing (which has been deformed due to the stress) relative to a stress-free sample. The Ultrasonic and Magnetic techniques exploit the acoustic and ferromagnetic properties of materials to perform relative measurements of residual stress. Non-destructive techniques include:

Neutron DiffractionSynchrotron DiffractionX-Ray DiffractionUltrasonicMagnetic

Non-destructive Techniques